Generally, a battery is widely classified into a chemical battery or a physical battery, and the chemical battery may also be classified into a primary battery, a secondary battery or a fuel cell. As the secondary battery, there are a Ni—Cd secondary battery, a Ni-Mh secondary battery, an SLA (sealed lead acid) secondary battery, a Lithium ion secondary battery, a Li-polymer secondary battery, a reusable alkaline secondary battery and the like.
Particularly, when the lithium ion battery is overcharged above a given voltage, a negative reaction may occur between a cathode active material and an electrolyte. Such a negative reaction destroys the structure of the cathode active material while causing an oxidation reaction of the electrolyte. In the meantime, lithium can be deposited on an anode active material. If the voltage applied to the secondary battery continuously rises even if the secondary battery has been overcharged, accidental ignition or explosion of the secondary battery may occur.
Conventionally, in order to prevent an overcharge of the Lithium ion secondary battery, a TS (thermostat) is connected between a power supply for providing a charging power and the Lithium ion secondary battery. If a temperature of the Lithium ion secondary battery rises above a predetermined temperature due to an overcharge, the thermostat turns off thereby to stop a charging operation.
In accordance with the prior art charging of the Lithium ion secondary battery is interrupted when the Lithium ion secondary battery is overheated due to the overcharge. Accordingly, although the Lithium ion secondary battery is fully charged, charging of the Lithium ion secondary battery is not interrupted since the Lithium ion secondary battery is not overcharged yet. Therefore, a life span of the Lithium ion secondary battery may be decreased.
Further, in accordance with the prior art, whether the Lithium ion secondary battery is overcharged or not is decided based on the temperature thereof Accordingly, in case of a high-temperature environment such as a tropical region or a low-temperature environment such as a polar region, it is difficult to decide whether the Lithium ion secondary battery is overcharged or not based on the temperature thereof Therefore, under such an environment, it is difficult to protect the Lithium ion secondary battery.
Therefore, it is strongly required to develop a technology capable of preventing the overcharge of the Lithium ion secondary battery regardless of an ambient temperature; and stopping charging the Lithium ion secondary battery when the Lithium ion secondary battery is fully charged or overcharged.